(a) Field of the Invention
The present invention relates to field emission displays (FEDs), and more particularly, to FEDs having carbon-based emitters.
(b) Description of the Related Art
A typical FED uses a cold cathode as the source for emitting electrons to realize the display of images. The overall quality of the FED depends on material and structural characteristics of the emitters that form an electron emitting layer. The first FEDs utilizing emitters were made mainly of molybdenum (Mo). Subsequently, Spindt-type metal tip (or microtip) emitters were developed.
However, in manufacturing the FED having metal tip emitters, it is necessary to form extremely minute openings into which the emitters are provided and necessary also to deposit Mo and uniformly form the metal microtips over an entire region of a screen. As a result, production is complicated, and highly precise technology process and expensive equipment are required for manufacture such that unit costs tend to increase. Further, the difficult processes involved make it difficult to manufacture FEDs of a large screen size.
Accordingly, much research and development is being performed by those in the FED industry to form emitters in a flat configuration that enable good electron emission at low voltage driving conditions and are relatively simple to manufacture. It is known that carbon-based materials, for example, graphite, diamond, diamond-like carbon (DLC), C60 (Fullerene), or carbon nanotubes (CNTs) are suitable for use in the manufacture of flat emitters. In particular, it is believed that CNTs, with their ability to realize favorable electron emission at relatively low driving voltages, is the ideal material for emitters in FEDs.
The FEDs using CNT technology typically employ a triode structure having cathodes, an anode, and gate electrodes. With these FEDs, cathode electrodes are first formed on a substrate. Then an insulating layer and gate electrodes including minute holes are deposited over the cathode electrodes. Emitters are then formed in the openings such that the emitters are positioned on the cathode electrodes.
However, with the FED having the above triode structure, a reduction in color purity occurs and it is difficult to realize sharp pictures. When the electrons emitted from the emitters form electron beams and travel toward phosphors, a diverging force of the electron beams is increased by a voltage (a positive voltage of a few volts to a few tens of volts) applied to the gate electrodes such that the electron beams scatter. The electron beams therefore land not only on the desired phosphors, but also on unintended phosphors to illuminate the same. Reduction in color results and sharp pictures become difficult to realize.
In order to prevent these problems, there are efforts to minimize the size of an emitter and deposit the emitter with the plural on an area corresponding to one phosphor such that scattering of the electron beams is minimized. However, there are limits to how small the emitters can be formed and problems occur with respect to phosphor illumination if the emitters are made too small. Difficulties with respect to focusing the electron beams also occur.
To prevent the scattering of the electron beams, a configuration in which additional electrodes for focusing the electron beams are mounted in the vicinity of the gate electrodes has been disclosed. However, such a structure is applied mainly to FEDs employing the microtip configuration and not to a structure of flat emitters, in which the resulting focusing effect is minimal.